1. Field of the Invention
The present invention relates generally to external counterpulsation cardiac assist devices, and more particularly, to external counterpulsation cardiac assist device pressure applicators having an outer shell that resists deformation.
2. Prior Art
In the existing external counterpulsation cardiac assist device (ECPCAD) applicators (hereinafter xe2x80x9capplicatorsxe2x80x9d); limb pressure is generated by inflating balloon-like chambers that surround the limb. In addition, to keep the volume of the inflow air in check, the balloon-like chambers are encased in a relatively non-extensible fabric to minimize the bulging out of the applicator assembly.
The longitudinal and transverse cross-sections of a typical applicator as mounted on a patient thigh are shown in FIGS. 1 and 2, respectively. In these illustrations, the limb 100 is encased in the outer shell 102. The space between the limb surface and the outer shell 102 is filled with a balloon 101. Such applicator designs with the outer shell 102 consisting of relatively non-extensible fabric type of material are currently in common use. The outer shell 102 of the applicator and its underlying balloon 101 are generally made wider than usually necessary, and while applying the applicator to the limb, it is overlaid to tightly cover the limb surface and is held in place by an extended VELCRO strap (not shown) or some other similar means.
The applicator is used by laying the patient on a bed, xe2x80x9cwrappingxe2x80x9d the applicator around the limbs, usually the legs, the thighs, arms, buttock, etc., and affixing the outer shell 102 by VELCRO or other similar means so that the assembly stays tightly over the limbs. Part of the limb such as the ankles, knees, feet, elbows, chest area, neck and the head are not covered since due to the absence of a considerable amount of muscle mass, no significant amount of blood can be displaced by the external pressure.
The amount of fluid (i.e., gas or liquid) that is required to operate each applicator is dependent on at least several factors.
Firstly, the amount of fluid that is required to operate each applicator is dependent on the initial volume (space) between the lining and the balloon and the balloon and the limb (if any) that has to be occupied by the expanding balloon. The effects of this factor is usually countered by attempting to wrap the applicator as closely to the limb surface as possible and leaving as little as possible space (volume or void space) to be filled by the balloon during the pressure application process. This precludes so-called rigid outer shells of various forms that have a fixed inner volume and are to be used on different patients with different limb geometry even though it may be attempted to fill at least part of the gap between the patients limb and such rigid outer shells using variously shaped and various material inserts. The process of filling such gaps is extremely cumbersome and cannot fill all the existing gaps since it is almost impossible to construct the required three-dimensionally shaped inserts, particularly in the presence of highly flexible balloons that are located between the xe2x80x9crigidxe2x80x9d outer shell and the limb.
The amount of fluid that is required to operate each applicator is also dependent on the amount of reduction in the volume of the segment of the limb that is enclosed by the applicator due to the applied pressure by the balloon and the level of limb surface pressure that has to be reached. These factors correspond to the desired and useful action of the applicator, which results in the blood pumping action of the device. The required airflow cannot therefore be reduced without reducing the volume of the blood that is displaced, thereby reducing the effectiveness of the applicator.
The amount of fluid that is required to operate each applicator is further dependent on the amount of increase in the applicator volume due to the expansion, bulging and change in the cross-sectional shape of its relatively non-extensible outer shell. This factor is indicative of the relative ease with which the outer shell of the applicator can expand and deform to allow its total internal volume (within which the encased segment of the limb is located) to increase with increased balloon generated internal pressure. This increase in the enclosed volume does not serve any purpose as far as the operation and performance of the applicator is concerned, and greatly reduces the efficiency of the applicator operation and it is the main source of increased demand on the air inflow to achieve the desired level of (limb) surface pressure during each cycle of its operation.
The amount of fluid that is required to operate each applicator is still further dependent on the volume of the soft tissue that may be pushed out of the sides of the applicator enclosure as the balloon is pressurized and pressure is applied to the limb segment. This factor also reduces the efficiency of the applicator by allowing some soft tissue mass to be pushed out of the enclosed volume, thereby reducing the volume of the displaced blood. In addition, the required volume of the air inflow to achieve the desired level of surface pressure is increased.
Lastly, the amount of fluid that is required to operate each applicator is still yet further dependent on the sliding of the shell down the limb towards a thinner section of the limb, thereby increasing the volume that has to be occupied by the expanding balloon. This factor greatly reduces the efficiency of the applicator by requiring a larger amount of air inflow to achieve the desired surface limb pressure.
Ideally, if the outer shell of the applicator is constructed to be rigid and to closely follow the contour of the enclosing limb surface (while allowing room for the pressure producing balloon), and prevented from shifting to the thinner side of the limb, the aforementioned increase in the internal volume of the applicator is almost totally eliminated. However, such rigid outer shells have to be constructed for each specific limb section of each individual to closely match their limb surface contour. Such relatively rigid applicator outer shells may be custom made using, for example various molding and rapid prototyping techniques known in the art, but with relatively high expense and by requiring an extended amount of time to produce the applicators for each individual patient.
Therefore it is an object of the present invention to provide a device and method for significantly reducing the aforementioned tendency of the outer shell of the applicator to expand and/or deform and thereby increase their internal volume as the internal balloon is pressurized.
Another objective of the present invention is to provide a device and method for minimizing the amount of soft tissue that is pushed out of the enclosed volume of the applicator.
Another objective of the present invention is to provide a device and method for minimizing the sliding of the applicator along the limb towards the thinner segments.
Accordingly, an applicator for applying an external counterpulsation to a body portion is provided. The applicator comprising: an outer shell for covering the body portion, the outer shell having a length in a longitudinal direction and a circumference in a circumferential direction; a balloon disposed in the outer shell, pressurization of which applies an external pressure to the body portion; and at least one anti-deformation member for reducing an amount of deformation of the outer shell caused by the pressurization of the balloon.
In a first preferred implementation, the at least one anti-deformation member preferably comprises a plurality of beam members disposed on an outer surface of the outer shell in the longitudinal direction. Preferably, the plurality of beam members are equally spaced along the circumference of the outer shell and at least one of the plurality of beam members has an I-beam cross-sectional shape.
Preferably, the plurality of beam members are disposed on the outer shell by threads that engage a portion of the beam members and a corresponding portion of the outer shell. Alternatively, the outer shell further comprises a pocket having an opening extending in the longitudinal direction for each of the plurality of beam members, wherein each of the plurality of beam members are disposed in a corresponding pocket. Preferably, the pockets are disposed on an outer surface of the outer shell. The pockets are preferably fastened to the outer shell by threads that engage a portion of the pockets and a corresponding portion of the outer shell.
At least one of the plurality of beam members preferably further comprises two or more beam segments, each of which are separated by a hinged joint to allow the beam member and outer shell to conform to a shape of the body portion in the longitudinal direction. Preferably, the hinged joint is a ball joint for allowing rotation of the beam segments in at least two directions. Alternatively, the hinged joint is a pinned joint for allowing rotation of the beam segments in a direction parallel to the longitudinal direction. The outer shell has a first and second end separated in the longitudinal direction by the length, wherein at least one of the plurality of beam members is preferably attached to the outer shell at each of the first and second ends.
In another preferred implementation, the applicator further comprises at least one transverse element disposed between at least two adjacent beam members of the plurality of beam members. Preferably, the at least one transverse element extends in the circumferential direction of the outer shell. The at least one transverse element can extend only in the circumferential direction or alternatively, the at least one transverse element comprises first and second transverse elements, the first and second transverse elements crisscrossing in the circumferential direction.
In another alternative, the at least one transverse element comprises a solid plate having a length substantially equivalent to the length of the outer shell. In another alternative, the at least one transverse element extends concavely in the circumferential direction.
In yet another alternative, the at least one anti-deformation member comprises constructing at least a portion of the outer shell with a plurality of truss elements which extend in the longitudinal direction. Preferably, each of the plurality of truss elements comprises a triangular truss element. The triangular truss elements preferably have a top and two angled sides, the top extends in the circumferential direction and the two angled sides extend in the longitudinal direction. The anti-deformation member preferably further comprises an outer sheet disposed on the tops of each of the triangular truss elements. Preferably the triangular truss elements and sheet member further comprise Velcro disposed between the tops and the outer sheet for connecting the outer sheet to the tops. Preferably, the plurality of truss elements are formed on a bottom sheet, the bottom sheet having a joint formed between adjacent truss elements. At least one of the joints is preferably a living joint formed in the bottom sheet.
In yet another preferred implementation, the applicator further comprises means for preventing tissue from bulging out from the first and second ends of the outer shell due to the pressurization of the balloon. Preferably, the means for preventing tissue from bulging out from the first and second ends comprises a collar disposed around the body portion adjacent each of the first and second ends. The collar preferably comprises a thin flexible material wrapped around the body portion adjacent each of the first and second ends to a desired height.
In still yet another preferred implementation the applicator further comprises means for preventing movement of the outer shell in the longitudinal direction. Preferably, the means for preventing movement of the outer shell in the longitudinal direction comprises a flexible material wrapped around both the first and second ends of the outer shell and the corresponding body portion adjacent the first and second ends. Where the applicator further comprises the means for preventing movement of the outer shell in the longitudinal direction, the means for preventing movement of the outer shell in the longitudinal direction preferably comprises a flexible material wrapped around both the first and second ends of the outer shell and the corresponding collars.
Also provided is a method for applying an external counterpulsation to a body portion. The method comprising: covering the body portion with an outer shell, the outer shell having a length in a longitudinal direction and a circumference in a circumferential direction; disposing a balloon in the outer shell; pressurizing the balloon to apply an external pressure to the body portion; and disposing at least one anti-deformation member in or on the outer shell for reducing an amount of deformation of the outer shell caused by the pressurization of the balloon.